The invention relates to a method for controlling swaying and swinging of a spreader in a crane and the load attached thereto, the crane comprising: a trolley, hoist gears provided with hoist drums placed in the trolley, hoisting ropes arranged on the hoist drums, on which the spreader is suspended from the trolley and which are directed back to the trolley through sheaves arranged on the spreader, whereby the swaying and swinging is controlled by control equipment comprising: four auxiliary gears provided with rope drums including motors and motor control equipment placed in the trolley, auxiliary ropes arranged on the rope drums of the auxiliary gears, sheaves for the auxiliary ropes placed in the spreader, through which sheaves the auxiliary ropes passing obliquely from the rope drums of the auxiliary gears are directed to spaces arranged in the hoist drums for the auxiliary ropes, and in which method the forces of the auxiliary ropes exerted on the spreader are controlled by moving the auxiliary ropes using the auxiliary gears by means of torque instructions obtained on the basis of the rope forces of the auxiliary ropes and the rotating speed data of the auxiliary gears using control logic that allows providing and maintaining the desired rope forces, controls the rotation and the resistance of the swinging of the motors in the auxiliary gears.
The method of the invention is known from Fl patent 101466, in which the method is presented in connection with a crane moving by means of rubber tyres and whose hoisting heights and hoisting speeds are moderate.
The method according to Fl patent 101466 adequately reduces the undesired movements of the load in the original applications thereof. Then again, in for instance the quay cranes moving on rails presented in Fl patent 108788, whose hoisting heights and moving speeds are significantly higher, the diagonal geometry of the auxiliary ropes and especially situations, in which the auxiliary ropes wound specifically on hoist drums move from one layer to another, require very rapid speed changes in the auxiliary gears. The control logic circuit presented in Fl patent 101466 is not fast enough for such a purpose.